VARIATIONS IN POTENCY 



Relative potency would, therefore, seem to be 

 a character inherited in Mendelian fashion. 1 



Observations of Coutagne on silk-moths may 

 be cited in support of this idea. Coutagne 

 made crosses between races of silk-moths dif- 

 fering in cocoon color, viz. between a race which 

 spun yellow cocoons and another one which 

 spun white cocoons. He found that some of 

 the Fj offspring spun yellow cocoons, others 

 white ones. The Fj yellow cocooned animals 

 when bred together produced F 2 progeny which 

 spun some yellow, others white cocoons, the 

 two sorts being as 3:1. In other words, yel- 

 low in such cases behaved consistently as a 

 dominant character. And the white-cocooned 

 Fj moths produced in F 2 cocoons of both colors, 

 but in this case the white cocoons were to the 

 yellow ones as 3:1. In other words, when 

 yellow behaved as a dominant in Fj it behaved 

 as a dominant also in F 2 ; and the same was 

 true of white. Each retained throughout the 

 two generations the relative potency with which 



1 It is of course possible to interpret such a case as due to the 

 separate inheritance of a factor which inhibits the development 

 of the character, but it is doubtful whether this line of explana- 

 tion can be successfully applied to cases presently to be described. 



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